This invention relates to a database search processor, and to a data processing system including such a search processor.
It is known to provide a dedicated search processor for performing searches through a database in response to search requests from a main (host) processor. For example, the search request may ask the search processor to find records in which specified fields match a specified search value. The advantage of using a dedicated search processor is that it reduces the load on the host, leaving the host free to perform other tasks. One example of a search processor is described, for example, in British Patent No. 1 497 676.
The search processor in the above reference consists of special-purpose logic, designed for the sole function of performing searches. Such a special-purpose logic can be very fast in operation, but is expensive to design and lacks flexibility. It would be more convenient if a search processor could be implemented using a general-purpose processor (e.g. a commercially available single-chip processor), suitably programmed to perform the required search function. However, there are problems in achieving a sufficiently high search rate using a general-purpose processor. For example, consider the case where it is required to perform an on-the-fly search on data from a disc file i.e. to search the data in real time as it arrives from the disc. The rate of data from a disc file is typically 2-4 million bytes/second. It has been found to be very difficult in practice to write a program which can search at this data rate and which is general enough to handle a variety of different search requests and a variety of different record formats.
The object of the present invention is to overcome or alleviate this problem.